The present invention relates to converting machines and, in particular to techniques for accomplishing butt splicing in converting machines.
Converting machinery is used to feed a web of paper, or other product from a roll to a using process. When the web on one roll expires, the leading edge of a web on a new roll must be attached. One way for attaching the leading edge includes shutting down and stopping the web, manually severing the tail end of the web from the expiring roll, and affixing the leading edge of the new roll. This procedure, of course, requires discontinuous feeding of the web to the using process.
In order to permit continuous feed from the roll to the using process, it is conventional to prepare a new roll by adding double-sided tape to its leading edge. As the expiring roll is nearly depleted, the new roll is rotated up to a peripheral speed equal to the web speed. A bump roll displaces the expiring web into contact with the double-sided tape, which adheres the leading edge of the web from the new roll to the moving web. Substantially simultaneously, a cutting bar is fired to sever the tail of the old web.
The type of splice above described is called a lap splice. That is, the location of the splice contains the expired web, the leading edge of the new web, and the double-sided tape between the two webs. Although many processes can tolerate lap splices, there are some which cannot. For example, when the web is relatively thick, the combined thicknesses of the two overlapped webs plus the double-sided tape may be more than the downstream using process can tolerate.
A butt splice is one in which the trailing edge of the expiring web is abutted, not overlapped, by the leading edge of the new web. One technique for practicing a butt splice on-the-fly is disclosed in U.S. Pat. No. 5,277,731, the disclosure of which is herein incorporated by reference. In that technique, a lap splice is first prepared, substantially as in the prior art described above. Then, the tail end of the expiring web, overlapped with the leading edge of the new web, is severed. The free tail end is diverted, so that the expiring and new webs ends abut each other, with single-sided tape joining the two webs. However, the original lap splice remains attached to the expiring web upstream of the cut. This original lap splice must be removed. This is done by a further cut in the expiring web to isolate the lap splice, together with leading and trailing portions of the expiring web, still attached to the butt-spliced web. Then, the lap splice must be removed. The disclosure of the ""731 patent suggests forming the lap splice using a double-sided tape of limited adhesive strength, so that its adherence is weak enough to be relatively easily overcome. One way suggested for disposing of the debris is to change the web direction sharply after butt splicing so that the butt splice and new web follow the changed direction, while the debris continues generally straight ahead. Separation is aided by a fixed blade.
In order to thicken the lap splice, and thus improve the ability to separate the debris, the above technique adds a length of stiff material between two layers of double-sided tape. This three-layer structure is then used to form the lap splice. Several disadvantages are foreseen in the prior-art technique. The certainty of separating the debris from the advancing web may be less that perfect. The amount of labor required to lay up two layers of double-sided tape plus the stiffening material exceeds that required for a simple lap splice, thereby increasing labor cost. Finally, the debris is quite bulky, thereby complicating disposal.
The prior-art technique is incapable of butt splicing a double-layer web in which the top layer of the expiring web is butt spliced to the top layer of the new web, and the bottom layer of the expiring web is butt spliced to the bottom layer of the new web.
Accordingly, it is an object of the invention to provide a butt splicer for converting machinery that overcomes the drawbacks of the prior art.
It is a further object of the invention to provide a butt splicer for converting machinery that lengthens the web path of a lap-spliced web, then severs the web before and after the lap splice so that, the lengthened path places the trailing end of the expiring web abutting the leading end of the new web. A single-sided tape is applied over the abutting ends to form the butt splice.
It is a still further object of the invention to form a butt splice in a two-layered web as described in the foregoing paragraph, and also to apply a single-sided tape over the abutting ends on the other side of the web. Thus, when the two-layer web leaves the butt splicer, the top layer of the expiring web is butt spliced to the top layer of the new web, and the bottom layer of the expiring web is butt spliced to the bottom layer of the new web. This permits downstream separation of the top and bottom layers by the using process.
Briefly stated, the present invention provides a butt splicer lengthens a travel distance of a lap-spliced web by a predetermined distance. A pair of knives, spaced apart by the predetermined distance are fired when the lap splice is between them. The severed ends of the web are brought together on a vacuum roll for the application of a tape bridging the upstream and downstream ends. In one embodiment, a second tape is applied to the second side of the web to form a double butt splice.
According to an embodiment of the invention, there is provided a butt splicer for butt splicing a web which contains a previously performed lap splice, comprising: first and second knives, the first and second knives being spaced apart a predetermined distance in a web-motion direction, means for lengthening a travel distance of the web between working positions of the first and second knives from an original travel distance by an amount equal to the predetermined distance, means for energizing the first and second knives when the lap splice passes therebetween to remove a waste portion of the web containing the lap splice, means for restoring the original travel distance of the web, whereby severed ends of the web are placed in abutment with each other, and means for applying a tape bridging the severed ends, whereby a butt splice is produced.
The above, and other objects, features and advantages of the present invention will become apparent from the following description read in conjunction with the accompanying drawings, in which like reference numerals designate the same elements.